Fluid pessure operable brake control valves

ABSTRACT

A triple valve for fluid operable braking is provided with an additional emergency braking valve portion which has its own pressure responsive member which is responsive to at least a predetermined reduction of brake pipe pressure relative to quick action chamber pressure in a given period of time to open a valve to apply pressure to the brake cylinder from a reservoir and to vent the brake pipe, the pressure responsive member having an arrangement of chokes such that on movement of the pressure responsive member away from the initial position a choke passage between the quick action chamber and brake pipe becomes more constricted.

United States Patent [191 Paginton 1 May 22, 1973 [54] FLUID PESSUREOPERABLE BRAKE [56] References Cited CONTROL VALVES UNITED STATESPATENTS lnvemerI Philip Norman Pagillwll, London, 1,895,464 H1933 Hewitt.303 37 x England 3,472,562 10/]969 Wahboum ..303/33 X [73] Assignee:Westinghouse l lrake and Signal Primary Examiner Duane Reger l dp y)Limited, London, Attorney-Larson, Taylor and Hinds g an 22 Filed: May28,1971 [571 ABSTRACT A tri 1e valve for fluid o erable brakin isrovided 21 A 1.N 147750 P P g P 1 pp 0 with an additional emergencybraking valve portion which has its own pressure responsive member which[30] Foreign Application Priority Data is responsive to at least apredetermined reduction of brake pipe pressure relative to quick actionchamber June 9, 1970 Great Britain ..27,923/70 pressure in a givenperiod of time to open a valve to apply pressure to the brake cylinderfrom a reservoir [52] US. Cl ..303/33, 303/8I and to vent the brakepipe, the pressure responsive [51] Int. Cl. ..B60t 15/22 member havingan arrangement of chokes such that [58] Field of Search ..303/33,37,39,43, or! movement of the pr r r p n ive member 3 3 9 81 away from theinitial position a choke passage SERVICE PORTION between the quickaction chamber and brake pipe becomes more constricted.

10 Claims, 2 Drawing Figures PATENTEL 3,734,575

sum 1 0f 2 SERVKE PORUON 5 FIG. 2. FIG. I. A

FLUID PESSURE OPERABLE BRAKE CONTROL VALVES This invention relates tofluid pressure operable brake control valve apparatus and relates moreespecially to an emergency braking control valve operable in response tomore than a predetermined rate and amount of change of a controllingfluid pressure to supplement a brake effort controlled by a servicevalve portion.

According to the present invention there is provided fluid pressureoperable brake control valve apparatus for controlling in response tobrake pipe pressure the supply of fluid under pressure into and out of abrake cylinder the apparatus including a pressure responsive memberseparating a chamber at brake pipe pressure from a chamber at a quickaction chamber reference chamber pressure, a choke being connected inseries between said chambers so dimensioned as to render the membermovably responsive only to at least a predetermined change of brake pipepressure in a given time to open a brake cylinder valve to provide inoperation a communication between a fluid pressure reservoir and a brakecylinder, the apparatus including means operable on movement of themember away from an initial position in a direction to open the brakecylinder valve, to effect closure of a choke varying valve to increasethe choke resistance which is effective during a subsequent movement inthe other direction towards the initial position.

The choke varying valve may be a valve which in the open conditionbypasses a choke in series with another fixed choke.

The means operable to effect closure of the choke varying valve maycomprise an actuator means which is mounted to the housing of theapparatus to urge the choke varying valve into its open position againsta spring when the pressure responsive member is in its said initialposition.

When used as an emergency valve portion, the movement of the pressureresponsive member of the apparatus preferably initially operates a ventvalve to vent brake pipe to atmosphere.

Further, movement of the pressure responsive member in the oppositedirection, during release operation,

past said initial position can be arranged to open an acceleratedrelease valve to connect brake cylinder and brake pipe.

The release valve may function moreover as a check valve to disconnectthe brake cylinder from the brake pipe when a predetermined pressuredifference exists between them.

In order that the invention may be more clearly understood and readilycarried into effect, the same will be further described by way ofexample with reference to FIGS. 1 and 2 of the accompanying drawingswhich together illustrate a control valve comprising an emergencyportion, a manifold portion and a service portion and the manner inwhich these portions are interconnected to constitute one embodiment ofthe invention as for operation referring to the drawings, the serviceportion, the manifold portion, and the emergency portion arecorrespondingly labelled and the manifold portion is provided with portsfor connection to brake pipe (BP), brake cylinder (BC), emergencyreservoir (ER), brake cylinder exhaust (EX) and auxiliary reservoir(AR).

The brake cylinder, emergency and auxiliary reservoirs are not shown butare assumed to be appropriately connected and as will be seen hereafter,the latter reservoirs are chargeable in the charging mode from the brakepipe (BP). The manifold portion also includes in addition to the variousairways to be referred to in greater detail hereafter, an air filter(AF) via which all incoming brake pipe air has to pass beforecommunicating with either of the pressure responsive members in theemergency portion or the service portion of the apparatus. The manifoldportion also includes a quick action chamber (QAC) further reference towhich will be made hereafter.

Referring now to the service portion, this bears considerable similarityto the brake control apparatus which is described in some detail in theSpecifications of co-pending Patent applications Ser. Nos. 115,650 and115,651. Certain detail differences will however become apparent. Forexample, the accelerated release reservoir of the above-numberedApplications is provided by the emergency reservoir of the presentembodiment. Further, associated with the auxiliary reservoir chargingvalve of the present arrangement, there is a further valve which isoperated from the same stem for charging the emergency reservoir. Also,retarded recharge valve means is provided associated with the auxiliaryreservoir charging stroke and a service portion inshot valve is providedwhich is operable to provide an inshot of air to the brake cylinder fromthe auxiliary reservoir upto a predetermined pressure of say 12 psi. Anemergency portion inshot valve is also similarly provided.

The service portion of the apparatus consists essentially of a mainpressure responsive member 1 slidably carried on a stem 2 in the housingof the service portion and the pressure responsive member 1 along withits flexible diaphragm 3 constitutes a partition between a chamber (b)which is connected to brake pipe and a chamber (a) which is connected toauxiliary reservoir. The pressure responsive member 1 carries a brakecylinder inlet valve represented by reference 4 and a brake cylinderexhaust valve represented by reference 5 each being operated by theupward or downward movement respectively of the pressure responsivemember. Also coupled to the member 1 is the auxiliary reservoir chargingvalve 6 and associated therewith an emergency reservoir charging valve7. Finally, the central stem 2 which is sealingly slidable in thehousing is coupled via a rod 8 to a quick service and inlet exhaustvalve assembly represented generally by the reference 9. The quickservice inlet and exhaust valve have a composite closure member 10 whichis seatable on the one hand against a lower piston operated slidablemember 11 and an upper slidable sleeve member 12. The quick serviceinlet and exhaust valve structure is the subject inter alia of the firstof the aforementioned copending Patent Applications.

As described previously in this last mentioned copending Application,the arrangement is provided with a quick service bulb capacity 14 whichis connected on the one hand to the underside of the stem 2, and on theother hand to the underside of the slidable member 11 which normallyrests in the position shown against a housed spring 15.

The brake cylinder exhaust valve 5 has its exhaust side connected via achoke 16 to one side of a pressure responsive member 17 the other sideof which is connected via an unimpeded passage R1 to the exhaust side ofthe valve 5. The pressure responsive member 17 operates a ball valve 18on exhausting of the brake cylinder to enable an accelerated release tooccur by virtue of a transient transfer of fluid pressure from theemergency reservoir to the brake pipe thereby assisting the release.This is described in more detail in the second of the above-mentionedco-pending Patent Applications, and the interconnections which areprovided inter alia via the further check valve 19 for achieving suchoperation will not be specifically pointed out further herein. The brakecylinder service inshot valve is shown in the drawings as valve 20 andthis is controlled by brake cylinder pressure by means of a pressureresponsive member 21 which is spring loaded by a spring 22 to hold thevalve 20 in an open position up to brake cylinder pressures of about 12p.s.i. In the closed position of the valve 20 above such pressures, thepassage between the auxiliary reservoir via the valve 4 and the brakecylinder is restricted to that through a choke 23. Also coupled to thebody of the inshot valve 20 and actuable by the pressure responsivemember 21 there is a brake cylinder maintaining valve 24 via which andchoke 26, the brake cylinder is connectible to the quick service bulbcapacity 14.

The retarded recharge valve to which reference has already been made, isrepresented by the valve and this again is operable via a rod by apressure responsive member 31 the underside of which is subject, in theposition of the service'portion shown, to auxiliary reservoir pressurevia the auxiliary reservoir charging valve 6. The pressure responsivemember 31 is spring loaded on the underside and the upper side isconnected to the auxiliary reservoir via the valve 6 through a choke 33.The path to the retarded recharge valve 30 from brake pipe is via acheck valve 34 or a choke 35 which is parallel with this check valve.

The emergency portion of the apparatus consists of a pressure responsivemember denoted generally by the reference which with a diaphragm 41provides separation between upper and lower chambers (q) and (p),respectively the upper chamber (q) being connected to the quick actionchamber (QAC) referred to previously and the lower chamber (p) isconnected via the air filter AF to the brake pipe BP. The pressureresponsive member 40 is mounted on a sealingly slidable rod 43 via whichon a downward movement it can cause opening of a vent valve member 44connected between the brake pipe via a coarse filter 45 and atmosphere.The valve 44 is normally biassed into the closed position by a spring 46and the valve member 44 is also sealingly slidable on an extension ofthe rod 43 which further engages an emergency accelerated release valvemember 47 which is also itself subject to a spring pressure effected bya spring 48 between members 44 and 47. The valve member 47 seats againsta slidable valve seat 49 via which when separated from 47 there is apassage between the brake cylinder and the brake pipe. The lower end ofthe slidable valve eat member 49 is engagable with a high pressure valveclosure member 50 which is spring biassed by the spring 51 into theclosed position in which it seals a path between the emergency reservoirand the brake cylinder.

A check valve 52 is provided between the quick action chamber and theemergency reservoir as indicated and also associated with the emergencyportion there is as mentioned previously an emergency inshot valve whichcomprises a valve closure member 53 which is maintained in an opencondition by the pressure of a spring 54 against a pressure responsivemember 55 the member 55 only being displaceable against the spring whenthe brake cylinder pressure has attained a value of approximately 12p.s.i. At this value, the valve closure member 53 is closable torestrict the path to the valves 57, 58 and 59. The valve 58 is the chokevarying valve and being centrally located is liftable off its seat inthe position of the member 40 as shown by a centrally disposed needle 60to provide a by-pass of a choke 62 via the check valve 57. Again, eachof the check valves 57 and 59 has a respective associated choke 63 and64. As will be seen hereafter, the check valve 59 operates as a quickaction chamber charging check valve and the check valve 57 serves as anovercharge dissipation check valve for the quick action chamber (QAC).

Referring now to the operation of the apparatus, it will be understoodat the outset, that the apparatus is required to control in response toapplied brake pipe pressure, the braking pressure applied from auxiliaryand/or emergency reservoirs, to a brake cylinder. The apparatus in thepresent instance is so designed as to control in response to a reductionof brake pipe pressure, an increase of braking pressure to the brakecylinder and vice versa. Release of the brakes is therefore achievableby a return of brake pipe pressures to a normal operating brake pipepressure. Furthermore, the apparatus is specifically designed for use ina vehicle which forms part of a train of further vehicles each havingidentical sets of braking apparatus connected to a common brake pipe.

Considering therefore the charging operation effected from the brakepipe when the brake pipe is pressurized from a drivers brake controlvalve, air from the brake pipe enters the apparatus at the port BP,passing via the air way B2 through the air filter AF, passages B3 and B4to the chamber (b) above the pressure responsive member 1 of the serviceportion. Brake pipe pressure also flows from the passage B3 via passageB5 into passage B7 and through the sensitivity check valve 34 to theretarded recharge valve 30 the position of which at this time is asshown due to the pressure of the spring 32. There is therefore a flow ofair via the valve 30 and the auxiliary reservoir charging choke 33 andthe air way A2 to the auxiliary reservoir charging valve 6 which is alsoin the open position and provides a passage via Al to the auxiliaryreservoir. The pressure in the auxiliary reservoir is also communicatedvia the air way A3 to the lower side (a) of the pressure responsivemember 1 of the service portion of the apparatus. By virtue moreover ofthe fact that auxiliary reservoir pressure is also applied from thepassage A2 to the lower side of the pressure responsive member 31 whichcontrols the retarded recharge valve 30, dependent upon the value of thespring 32, the valve 30 can maintain a substantially constantdifferential across the charging choke 33. This assists uniform chargingthroughout a train of vehicles connected to a common brake pipe.

Brake pipe air is also applied from the passage B5 referred to above tothe passage B6 which is connected to the underside of the quick servicevalve of the service portion and a passage for brake pipe air is alsoprovided via a coarse filter 45 and the air way B1 to the region beneaththe vent valve 44 referred to above. Additionally, air from the brakepipe via the filter AF can flow via the passage B8 to the chamber (p)beneath the pressure responsive member 40. Air from the chamber (p) thenflows via the charging choke 64 and the quick action chamber chargingcheck valve 59 to the quick action chamber via the air way (q).

Charging of the emergency reservoir which is connected at the point ERof the manifold portion of the apparatus is effected from the auxiliaryreservoir via the passage A1 leading to the valve 6, the charging checkvalve 7, and the airway E4 into the airway E3 connected to the emergencyreservoir. It will be appreciated therefore that emergency reservoirpressure is applied'via the check valve 19 to the upper side of theaccelerated release valve 18 and the emergency reservoir thereforeconstitutes a source of accelerated release air for the operation of theaccelerated release valve.

When the system is fully pressurized and a stable condition exists, thepressure differential which is effective on the pressure responsivemember 1 of the service portion due to brake pipe pressure acting overthe area of the stem 2 against atmospheric pressure which at this timeis present in the quick service bulb 14 due to the quick service exhaustvalve being open, maintains the service portion in the position shown.In this position, the valve 5 is in the position shown and the brakecylinders are therefore vented to atmosphere and the accelerated releasevalve 18 rests in the closed position due to the slight downward thrustprovided by the pressure responsive member 17.

Ignoring for the present, the operation of the emergency portion andindeed, assuming that the brake pipe pressure is controlled at acontrolled rate such that the emergency portion does not operate, thepressure in the chamber (b) above the pressure responsive member l ofthe service portion is reduced and the differential causes the pressureresponsive member to rise against the stabilizing pressure of the mainstem. Such movement causes the quick service inlet valve 10 to lift fromits slidable valve seat which is held down against the housed spring bythe brake pipe pressure in the passage B6. Opening of the valve 10allows brake pipe air to flow into the quick service bulb capacity 14via passages B5, B6 and S1 and S2 and there is a consequential immediatedrop of pressure above the pressure responsive member 1 in the chamber(b). The pressure responsive member therefore tends to move up morerapidly and the quick service bulb capacity 14 is sealed off fromatmosphere by engagement of the valve member 10 with the slidable valveseat 11. The pressure across the quick service control piston at thelower end of the slidable member 11 then equalizes and this permits thelight spring loading to cause the member 11 to move up to its uppermostposition. In this position, the quick service inlet valve is not closedbecause the upward movement of the main stem has carried with it theslidable portion 12 to a point at which the portion 12 engages with itsupper stop, at which point the valve seat 10 is separated from theslidable member 11. The upward movement of 12 is achieved and maintainedby virtue of the bulb pressure acting on the area of the valve plus thesleeve 12, as compared with atmospheric pressure which exists in thequick service bulb exhaust passage.

During the rapid upward movement of the pressure responsive member 1 andthe stem 2, the brake cylinder exhaust valve 5, the auxiliary reservoircharging valve 6 and the emergency reservoir charging valve 7 close,followed by the opening of the brake cylinder inlet valve 4. Auxiliaryreservoir air therefore flows via the passage A3, the chamber (a)beneath the pressure responsive member 1 and the brake cylinder inletvalve 4 to the service inshot valve 20 which is open and therefore thisair flows to the brake cylinder via the passages A5, A6, A7, AS, theemergency inshot valve 53 in the open condition, the passage C1 to thebrake cylinder BC. As mentioned previously both inshot valves 20 and 53remain in the open condition until the brake cylinder pressure hasattained a pressure of approximately 12 p.s.i. At this point the inshotvalves close and reduce the initially large opening to the brakecylinder to a passage which is controlled by the choke 23 associatedwith the service inshot valve or the choke 56 associated with theemergency inshot valve as the case may be.

The rise of brake cylinder pressure depends upon the degree of reductionin brake pipe pressure and if the brake pipe reduction is not sufficientto produce the required pressure, the brake cylinder maintaining valve24 does not close and the connection exists between the quick servicebulb l4 and brake pipe and the brake cylinder via passages S2, S3, choke26, and the valve 24 to the brake cylinder via passage A6 and theemergency portion. Brake pipe pressure is therefore reduced by flow intothe brake cylinder until sufficient brake cylinder pressure is producedto deflect the pressure responsive member 21 to close the inshot valveand the brake cylinder maintaining valve.

It is to be understood that the foregoing description of operationassumes that the rate of reduction of brakepipe pressure is insufficientto deflect the pressure responsive member 40 of the emergency portion,the quick action chamber pressure flowing back into the brake pipe viathe choke 63 and the check valve 57 causing the pressure differentialacross the pressure responsive member to not be sufficient to deflectthe member 44 against the spring 46.

Release after a service application as indicated above, is effected bythe drivers brake valve producing a recovery of brake pipe pressuretowards the normal steady value. If therefore the brake pipe pressure isso increased, a pressure differential is produced across the pressureresponsive member 1 of the service portion of the apparatus to cause adownward force which is resisted by the upward force of brake pipepressure in the bulb capacity 14 on the quick service valve member 10and the underside of the stem 2. As soon as this force is overcome, thepressure responsive member moves downwards and the sleeve member 12 ofthe quick service valve arrangement descends until it reaches its loweststop by which time the valve closure member 10 is in engagement with theslidable sleeve 11 so that the quick service inlet valve is closedbefore the quick service exhaust valve is opened. This ensures thatduring the releasing operation, there is no communication in the quickservice valve arrangement between the brake I pipe, the quick servicebulb capacity and atmosphere. Further increase in the pressuredifference across the diaphragm is thus effected by exhausting of thebulb pressure under the stem 2 and such increase in pressuredifferential causes rapid downward movement of the pressure responsivemember to open the brake cylinder exhaust valve 5, the auxiliaryreservoir charging valve 6, and the emergency reservoir charging valve7. Re-

leasing brake cylinder air flows to atmosphere via the airway A6, thevalve 5 and the exhaust passage R1. The exhaust pressure in the passageR1 operates beneath the pressure responsive member 17 of the acceleratedrelease valve 18 and the member 17 therefore temporarily moves upwardsto provide a communication between the emergency reservoir whosepressure is above the valve 18 and the brake pipe. By virtue of thechoke 16, the pressure after a short interval equalizes across thepressure responsive member 17 and the valve 18 recloses. Operation ofthe accelerated release valve 18 for this brief interval assists therapid propogation of a brake release along a train by the flow ofemergency reservoir air into the brake pipe augmenting increase of brakepipe pressure from the drivers brake valve.

It will be further noted that since the pressure in the quick servicebulb capacity 14 is now vented via the quick service vent valve 10, thebulb pressure beneath the piston of the slidable sleeve 11 falls and thepiston is held against the housed spring in the position shown in thedrawing. The release position is thus regained in which the pressureresponsive member 1 and the components beneath it are urged downwardsagainst this housed spring by the resultant of brake pipe pressure inthe chamber (b) over the area of the stem 2 against atmospheric pressurein the quick service bulb 14.

The operation has been described so far on the assumption that the ratesof change of brake pipe pressure have been only sufficient to causeoperation of the service portion of the apparatus but if the brake pipepressure is rapidly dropped as for an emergency brake application, thereduction of brake pipe pressure effective in the chamber (p) beneaththe pressure responsive member 40 of the emergency portion of theapparatus is more rapid than can be compensated for by flow of air viathe choke 63 and the check valve 57. The upward force of brake pipepressure in the passage B1 and the force of the spring 46 beneath thevent valve 44 is therefore overcome and the pressure responsive membermoves downwards to open the vent valve 44. The brake pipe pressure istherefore rapidly vented to atmosphere via the passage B1 and the openvalve 44. The pressure responsive member and stem 43 continue to movedownwards to fully open the high pressure valve 50 to connect theemergency reservoir via the passage E2 to the emergency inshot valve 53,the open condition of which permits this emergency reservoir air to beapplied directly to the brake cylinder at BC.

It will be appreciated moreover that the action of brake pipe pressurealso enables the service portion described above to operate in themanner of a service application and supply air from the auxiliaryreservoir to the brake cylinder. Under an emergency applicationtherefore the auxiliary reservoir air is supplemented by emergencyreservoir air to eflect a rapid application. Also, the operation of theemergency portion can be arranged to provide a 20 percent (say) increasein the pressure in the brake cylinder as compared with that which isproduced for a given reduction of brake pipe pressure purely by theservice portion.

As mentioned previously, the inshot valve 53 is arranged by virtue ofthe spring pressure of the spring 54 and the dimensioning of thepressure responsive member 55 to remain open until brake cylinderpressure attains approximately 12 p.s.i. The build up of air in thebrake cylinder for an emergency application is therefore very rapid tobegin with following sufficiently rapid drop of brake pipe pressureuntil the point at which the valve 53 closes. After this time a build upof brake pipe pressure is governed by the choke 56.

Downward movement of the pressure responsive member 40 of the emergencyportion causes the valve ball 58 to lift off the needle 60 so that thechoke 63 is no longer by-passed via the valve 58 and the flow of airbetween the chambers (q) and (p) on either side of the pressureresponsive member can only pass via the chokes 62 and 63 in series withthe check valve 57. This enables a clean and rapid function such thatthe vent valve 44 is held open for a prolonged time until the quickaction chamber pressure falls to a lower value at which the spring 46can reclose the vent valve 44 and also permit the high pressure valve 50to close interrupting the communication between brake cylinder andemergency reservoir.

The sequence of events during a brake release operation following arapid reduction of brake pipe pressure which has given rise to operationof the emergency portion as described above may now be considered. Whenthe brake pipe pressure is recharged, it is effective in the chamber (p)to permit upward movement of the pressure responsive member 40 againstthe housed spring shown above it. This permits the emergency acceleratedrelease valve 47 to lift off its seat provided on the sliding member 49and thereby provides a path from on the one hand the brake cylinder andon the other hand the auxiliary reservoir via the open brake cylinderinlet valve 4 of the service portion to flow to the brake pipe viapassages A7 and A8. An accelerated" build up of brake pipe pressure isthereby effected and since the auxiliary reservoir pressure is therebyalso reduced the service portion operates to a release condition at anearlier instant in time since brake pipe pressure is required to recoverto a lower pressure to effect movement of the pressure responsivemember 1. The emergency accelerated release valve 47 in conjunction withits spring 48 operates as a check valve such that it recloses when theauxiliary reservoir and brake cylinder pressures have attained valueswithin approximately 10 p.s.i. of the brake pipe pressure. Subsequently,the pressures in the chambers (p) and (q) move towards one another byvirtue of the choke 64 and check valve 59 and the member 40 returns to aposition as shown in the drawing. It will be appreciated that asubstantial reduction of auxiliary reservoir pressure is experiencedduring an emergency operation and recharging of the auxiliary reservoiris effected as described previously via the service portion auxiliaryreservoir charging valve and the retarded recharge valve 30 affords acontrolled recharge by enabling a fixed pressure differential to beproduced across the choke 33 as described previously. Similarly,recharging of the emergency reservoir is effected as described beforevia the valve 7.

In order that a typical manner of operation may readily be envisaged onthe basis of the foregoing description, it may for example be visualizedthat the normal running brake pipe pressure may be 70 p.s.i. and thepressure responsive member of the service portion moves towardsapplication of brakes when the brake pipe pressures falls below 0.75p.s.i. of the auxiliary reservoir pressure. The service portionsubsequently laps off to a stable lap position with brake cylinder valveclosed when the brake pipe is at approximately auxiliary reservoirpressure.

The volumes may typically be so designed moreover that under serviceapplication conditions, a drop of brake pipe pressure of 20 p.s.i. willgive a full service brake application of 50 p.s.i. brake cylinderpressure. Intermediate higher brake pipe pressures provide intermediatelower brake cylinder pressures.

Brake release under service application conditions is effected by a riseof brake pipe pressure of 1.5 p.s.i. above the auxiliary reservoirpressure, this being sufficient to cause downward movement of thepressure responsive member 1 from the lap position towards a position toopen the brake cylinder exhaust valve.

If the rate of fall of brake pipe pressure on application conditions issufficient and fast enough, the emergency portion operates with theservice portion to enhance the brake cylinder pressure to produce anemergency brake application.

Typically the choke 63 and the check valve 57 of the emergency portionare so dimensioned that a drop of brake pipe pressure from 70 to 50p.s.i. in 2 seconds will cause an emergency operation by opening ventvalve 44 whereas a drop of from 70 to 50 p.s.i. in three seconds willcause only a service application. Additionally, small reductions ofbrake pipe pressure, of say 8 p.s.i. or less will not of themselvesalone, however fast, effect the emergency portion.

After an emergency application, a reset time for the vent valve isarranged by choice of chokes 62 and 63, to be of the order of oneminute. Additionally, recharge of the emergency portion is arranged tobe fully effected from to 70 p.s.i. via choke 64 in approximately oneminute.

I claim:

1. Fluid pressure operable brake control valve apparatus forcontrolling, in response to brake pipe pressure, the supply of fluidunder pressure into and out of a brake cylinder, the apparatus includinga housing having a first chamber at brake pipe pressure and a secondchamber at reference pressure, a fluid pressure responsive memberseparating the first and second chambers, choke means connected betweensaid chambers, a brake cylinder valve connected between a fluid pressurereservoir and a brake cylinder port, a vent valve connected between abrake pipe port and an exhaust port, means linking both said valves tothe pressure responsive member so as to be opened by movement of thepressure responsive member when a fall of brake pipe pressure inrelation to the reference pressure is sufficiently rapid as to be notcompensated for by fluid flow in the choke means, said choke meansincluding a choke varying valve, and actuator means for adjusting thechoke varying valve in the sense to increase the choke resistance tofluid flow upon said movement of said pressure responsive memberconsequent on a fall of brake pipe pressure of said sufficient rapidity.

2. Brake control valve apparatus as claimed in claim 1, wherein saidchoke means comprises first and second series connected chokes, and saidchoke varying valve controls a by-pass around said first choke.

3. Brake control valve apparatus as claimed in claim 2 furthercomprising a check valve in series with said first and second chokes forallowing fluid pressure movement from the reference pressure chambertoward the brake pipe pressure chamber when said choke varying valve isin the closed position.

4. Brake control valve apparatus as claimed in claim 3, furthercomprising a third choke between said chambers, and a charging checkvalve to permit charging of the reference pressure chamber from thebrake pipe pressure chamber through said third choke.

5. Brake control valve apparatus as claimed in claim 4, wherein thechoke varying valve and the first and second chokes are mounted to thepressure responsive member, and the choke varying valve actuator meansis fixed to the housing of the apparatus so as to effect opening andclosing of the choke varying valve as a consequence of movement of saidpressure responsive member.

6. Brake control valve apparatus as claimed in claim 1, furthercomprising an accelerated release valve connected between the brakecylinder port and the brake pipe and so mechanically coupled to thepressure responsive member as to be opened when a recovery of brake pipepressure in the first chamber beyond a reduced reference pressure in thesecond chamber takes place after reclosure of the brake cylinder valveand the bent valve.

7. Brake control valve apparatus as claimed in claim 6, wherein the ventvalve, the brake cylinder valve and the accelerated release valve areall disposed in an inline arrangement.

8. Brake control valve apparatus as claimed in claim 7, wherein theaccelerated release valve comprises a closure member and a seat whichare movable as one in the closed position thereof, and the brakecylinder valve being operable by the pressure responsive member via anactuating rod and the movable accelerated release valve.

9. Brake control valve apparatus as claimed in claim 8, furthercomprising resilient means for resiliently urging the acceleratedrelease valve toward the closed position in the release position of theapparatus in order that it operates as a check valve during brakerelease operation and closes at a predetermined value of pressuredifference between the brake pipe and the brake cylinder.

10. Brake control valve apparatus as claimed in claim 1, in combinationwith a service application controlling triple valve responsive to lessthan said predetermined change of brake pipe pressure.

* =l= l= a

1. Fluid pressure operable brake control valve apparatus forcontrolling, in response to brake pipe pressure, the supply of fluidunder pressure into and out of a brake cylinder, the apparatus includinga housing having a first chamber at brake pipe pressure and a secondchamber at reference pressure, a fluid pressure responsive memberseparating the first and second chambers, choke means connected betweensaid chambers, a brake cylinder valve connected between a fluid pressurereservoir and a brake cylinder port, a vent valve connected between abrake pipe port and an exhaust port, means linking both said valves tothe pressure responsive member so as to be opened by movement of thepressure responsive member when a fall of brake pipe pressure inrelation to the reference pressure is sufficiently rapid as to be notcompensated for by fluid flow iN the choke means, said choke meansincluding a choke varying valve, and actuator means for adjusting thechoke varying valve in the sense to increase the choke resistance tofluid flow upon said movement of said pressure responsive memberconsequent on a fall of brake pipe pressure of said sufficient rapidity.2. Brake control valve apparatus as claimed in claim 1, wherein saidchoke means comprises first and second series connected chokes, and saidchoke varying valve controls a by-pass around said first choke.
 3. Brakecontrol valve apparatus as claimed in claim 2 further comprising a checkvalve in series with said first and second chokes for allowing fluidpressure movement from the reference pressure chamber toward the brakepipe pressure chamber when said choke varying valve is in the closedposition.
 4. Brake control valve apparatus as claimed in claim 3,further comprising a third choke between said chambers, and a chargingcheck valve to permit charging of the reference pressure chamber fromthe brake pipe pressure chamber through said third choke.
 5. Brakecontrol valve apparatus as claimed in claim 4, wherein the choke varyingvalve and the first and second chokes are mounted to the pressureresponsive member, and the choke varying valve actuator means is fixedto the housing of the apparatus so as to effect opening and closing ofthe choke varying valve as a consequence of movement of said pressureresponsive member.
 6. Brake control valve apparatus as claimed in claim1, further comprising an accelerated release valve connected between thebrake cylinder port and the brake pipe and so mechanically coupled tothe pressure responsive member as to be opened when a recovery of brakepipe pressure in the first chamber beyond a reduced reference pressurein the second chamber takes place after reclosure of the brake cylindervalve and the bent valve.
 7. Brake control valve apparatus as claimed inclaim 6, wherein the vent valve, the brake cylinder valve and theaccelerated release valve are all disposed in an in-line arrangement. 8.Brake control valve apparatus as claimed in claim 7, wherein theaccelerated release valve comprises a closure member and a seat whichare movable as one in the closed position thereof, and the brakecylinder valve being operable by the pressure responsive member via anactuating rod and the movable accelerated release valve.
 9. Brakecontrol valve apparatus as claimed in claim 8, further comprisingresilient means for resiliently urging the accelerated release valvetoward the closed position in the release position of the apparatus inorder that it operates as a check valve during brake release operationand closes at a predetermined value of pressure difference between thebrake pipe and the brake cylinder.
 10. Brake control valve apparatus asclaimed in claim 1, in combination with a service applicationcontrolling triple valve responsive to less than said predeterminedchange of brake pipe pressure.